For safety, the transmission of electrical power requires that the transmission lines, whatever the voltage being transmitted, have grounding connections to minimize or eliminate unforeseen static charge build-up or power surge from outside forces, such as lightning strikes on the transmission lines, towers or poles. In the instances where the electrical power is being supplied to a residence or office or business building, adequate grounding can usually be made by utilizing the water supply line laid in the earth. Where a large quantity of voltage is involved, it is customary to use an approved grounding rod, normally a nominal 5/8 inch in diameter and of a length of 8 to 10 feet. In some areas of the country rods of a nominal 1/2 inch are used and those rods are normally galvanized steel. The 158 inch rods are galvanized steel or copper cladded steel rods. A single rod such as this is usually driven into the ground using a hand-operated driving hammer such as disclosed in U.S. Pat. Nos. 4,557,409 and 4,315,551.
However, in many areas of the country it is necessary to drive grounding rods to a depth greater than the length of one rod. When it is necessary to drive two or more grounding rods into the earth to achieve appropriate grounding the successive rods must be mechanically coupled to ensure continuing electrical contact. Such coupling is done by employing one or more special coupling units which may be generally described as a sleeve of electrically conductive metal having an interior of a plurality of lands and grooves, the sleeves having opposing exterior end of diametrical openings slightly in excess of the normal diameter of the driving rod with an inwardly tapering bore having a diameter slightly less than the nominal diameter of the grounding rod. For such couplings, standard in the industry, to be usable it is imperative that the end of the grounding rod being impacted to insert the rod insertor into the earth not be deformed to a diameter greater than the diameter of the exterior opening of the connecting sleeve, referred to as "mushrooming" in the trade.
Tests using the electrical rod driver disclosed in FIG. 2 of U.S. Pat. No. 4,315,551 in driving rods into frozen earth resulted in the "cold weld" capture of the grounding rod. This means destruction of this driver in order to accommodate the coupling previously mentioned. The driver shown in FIG. 4 of this patent was not available for testing. However, experience in this field and analysis of the "accept all diameters of rods" shown in FIG. 4 results in the technical conclusion that the driven end of the rod within FIG. 4 recess may not result in a "cold weld" of the driven end but the so-driven drive result will be an increased diameter of the driven end of the rod to the extent that the standard coupling for joining successive driven rods cannot be used. The only solution in such a situation is to use the labor intensive, time-consuming welding of the two rod ends which may not be permanent in view of the continuous successive power blows upon the rod end. The alternative would be to cut the end of the grounding rod welded in the interior of the driving device previously described and install the so-cut end into one side of the aforementioned coupling device and place this coupling over the end of the grounding rod next to be inserted into the earth. Depending upon the resistive nature of the ground, such as frozen ground or very dense, compacted clay soils, hand-driving is not practical nor effective. In such instances it is necessary to use powered driving means, usually operated by a pressurized fluid such as a commercial impact hammer. When more than one rod is required to obtain the desired grounding, successive rods are driven in, coupled together and the procedure continued until the required grounding is obtained.
Up to the present time, such rods are driven into the earth by continuously impacting the upper end of the rod with a vertically reciporcating impact hammer. Such multiple impacting on the top of the rod, particularly in frozen soil or compacted clay soil tends to "upset" or "mushroom" the rod end to the degree that the couplings in use could not be fitted over the "upset" end. To permit use of a coupling in such instance, it was necessary to cut off the upset end of the rod. To overcome such upsetting of the rod end and necessary removal of the upset end of the rod the anvil head was provided with a cylindrical bore of a fractionally greater diameter to receive the end of the rod and hopefully to limit the mushroom formation of the rod end as disclosed in U.S. Pat. No. 4,315,551. Such fractional diametrical difference continued to allow the end of the rod to be upset under deep driving conditions with the result that the end of the rod in the bore which terminates in a cupola effected a cold weld with the anvil head that made it impossible to separate the rod from the anvil, again requiring the rod to be cut off and installing a new driving anvil for each successive rod.
This patent also discloses an anvil with a rod-receiving bore which can accommodate a plurality of rod diameters. Experience in the field indicates that the anvil bore must firmly hold the rod being driven and not permit any wobbling within the bore.